Bottom Line:
We study the effect of global and local dielectric variations on the polarization conversion rps response of ordered nickel nanowires embedded in an alumina matrix.When considering local changes, we observe a non-monotonous behavior of the rps, its intensity unusually modified far beyond to what it is expected for a monotonous change of the whole refractive index of the embedding medium.This is related to the local redistribution of the electromagnetic field when a localized surface plasmon is excited.

ABSTRACTWe study the effect of global and local dielectric variations on the polarization conversion rps response of ordered nickel nanowires embedded in an alumina matrix. When considering local changes, we observe a non-monotonous behavior of the rps, its intensity unusually modified far beyond to what it is expected for a monotonous change of the whole refractive index of the embedding medium. This is related to the local redistribution of the electromagnetic field when a localized surface plasmon is excited. This finding may be employed to develop and improve new biosensing magnetoplasmonic devices.

Figure 3: Intensity (a) and spectral position (b) of the /rps/ peak. As a function of a shell thickness. Dots (circles) correspond to a system composed of Ni nanowires embedded in an n = 1.7 (n = 1.4) dielectric medium and surrounded by an n = 1.4 (n = 1.7) shell. The black and dotted horizontal lines correspond to the values for the n = 1.7 and n = 1.4 uniform backgrounds respectively.

Mentions:
In this respect, the localization of the EM field at the plasmonic resonance allows studying its influence on the polarization conversion response to local dielectric changes in the dielectric matrix, which may find important applications in biosensing [19]. To do so, we considered a cylindrical shell, surrounding the nanowire with a different refractive index to that of the embedding matrix. The effects of the shell were studied for different thicknesses, from 0 nm (no shell) to 50 nm (neighboring shells in contact), and for different dielectric values: (a) n = 1.4 (n = 1.7 for the matrix) and (b) n = 1.7 (n = 1.4 for the matrix). Figure 3a, b shows the spectral position and intensity of the /rps/ peak as a function of the shell thickness for the different (a) and (b) dielectric environments (dots and circles, respectively). The black and dotted horizontal lines correspond to the values for the n = 1.7 and n = 1.4 uniform dielectric backgrounds, respectively. For both dielectric environments, the spectral position of the /rps/ peak (see Figure 3a) shifts almost linearly with the shell thickness. On the contrary, the evolution of its intensity does not appear to happen in a linear way. For example, if we restrict to the first case (a), a 5-nm shell around the wires implies a strong decrease of the intensity for the /rps/ peak. A 20-nm shell leads to the maximum decrease, and beyond this thickness, the value of /rps/ approaches gradually to that of the uniform dielectric medium. On the other hand, case (b) shows that the intensity increases above the values for the two uniform backgrounds, being the 15-nm thick shell the one that leads to the maximum /rps/. It is worth noticing that in both cases, there is a range of shell thicknesses in which the value of /rps/ exceeds that obtained if the whole embedding matrix had the same refractive index of the shell. In particular, if we assume that replacing the whole refractive index of the matrix represents a 100% variation of the /rps/, then the optimum shell thicknesses for cases (a) and (b) represent more than a 200% variation of the /rps/. It is also remarkable that employing other materials presenting a larger difference in their refractive indexes might provide a much intense variation of the /rps/. However, in our case, we have tried to remain as realistic as possible, employing refractive indexes that have already measured in the fabrication of alumina templates [20].

Figure 3: Intensity (a) and spectral position (b) of the /rps/ peak. As a function of a shell thickness. Dots (circles) correspond to a system composed of Ni nanowires embedded in an n = 1.7 (n = 1.4) dielectric medium and surrounded by an n = 1.4 (n = 1.7) shell. The black and dotted horizontal lines correspond to the values for the n = 1.7 and n = 1.4 uniform backgrounds respectively.

Mentions:
In this respect, the localization of the EM field at the plasmonic resonance allows studying its influence on the polarization conversion response to local dielectric changes in the dielectric matrix, which may find important applications in biosensing [19]. To do so, we considered a cylindrical shell, surrounding the nanowire with a different refractive index to that of the embedding matrix. The effects of the shell were studied for different thicknesses, from 0 nm (no shell) to 50 nm (neighboring shells in contact), and for different dielectric values: (a) n = 1.4 (n = 1.7 for the matrix) and (b) n = 1.7 (n = 1.4 for the matrix). Figure 3a, b shows the spectral position and intensity of the /rps/ peak as a function of the shell thickness for the different (a) and (b) dielectric environments (dots and circles, respectively). The black and dotted horizontal lines correspond to the values for the n = 1.7 and n = 1.4 uniform dielectric backgrounds, respectively. For both dielectric environments, the spectral position of the /rps/ peak (see Figure 3a) shifts almost linearly with the shell thickness. On the contrary, the evolution of its intensity does not appear to happen in a linear way. For example, if we restrict to the first case (a), a 5-nm shell around the wires implies a strong decrease of the intensity for the /rps/ peak. A 20-nm shell leads to the maximum decrease, and beyond this thickness, the value of /rps/ approaches gradually to that of the uniform dielectric medium. On the other hand, case (b) shows that the intensity increases above the values for the two uniform backgrounds, being the 15-nm thick shell the one that leads to the maximum /rps/. It is worth noticing that in both cases, there is a range of shell thicknesses in which the value of /rps/ exceeds that obtained if the whole embedding matrix had the same refractive index of the shell. In particular, if we assume that replacing the whole refractive index of the matrix represents a 100% variation of the /rps/, then the optimum shell thicknesses for cases (a) and (b) represent more than a 200% variation of the /rps/. It is also remarkable that employing other materials presenting a larger difference in their refractive indexes might provide a much intense variation of the /rps/. However, in our case, we have tried to remain as realistic as possible, employing refractive indexes that have already measured in the fabrication of alumina templates [20].

Bottom Line:
We study the effect of global and local dielectric variations on the polarization conversion rps response of ordered nickel nanowires embedded in an alumina matrix.When considering local changes, we observe a non-monotonous behavior of the rps, its intensity unusually modified far beyond to what it is expected for a monotonous change of the whole refractive index of the embedding medium.This is related to the local redistribution of the electromagnetic field when a localized surface plasmon is excited.

ABSTRACTWe study the effect of global and local dielectric variations on the polarization conversion rps response of ordered nickel nanowires embedded in an alumina matrix. When considering local changes, we observe a non-monotonous behavior of the rps, its intensity unusually modified far beyond to what it is expected for a monotonous change of the whole refractive index of the embedding medium. This is related to the local redistribution of the electromagnetic field when a localized surface plasmon is excited. This finding may be employed to develop and improve new biosensing magnetoplasmonic devices.